From dbs@gemini.gsfc.nasa.gov Fri Aug 18 16:42:19 EDT 2000 Received: from gemini.gsfc.nasa.gov (gemini.gsfc.nasa.gov [128.183.107.53]) by leo.gsfc.nasa.gov (8.9.3/8.9.3) with ESMTP id QAA12067; Fri, 18 Aug 2000 16:42:18 -0400 (EDT) Received: (from dbs@localhost) by gemini.gsfc.nasa.gov (8.9.3/8.9.3) id QAA08617; Fri, 18 Aug 2000 16:42:17 -0400 (EDT) Date: Fri, 18 Aug 2000 16:42:17 -0400 (EDT) From: Dave Shaffer Message-Id: <200008182042.QAA08617@gemini.gsfc.nasa.gov> To: dbs@leo.gsfc.nasa.gov, pet@leo.gsfc.nasa.gov Subject: Re: 0839+187 Cc: kopeikins@missouri.edu Status: R Leonid, Here's some information about 0839+187, along with where to find it, so you and your friends can check directly (which I suggest). The best places to find recent information about (relatively) compact sources are 1) The VLA calibrator manual 2) The list(s) of sources originally developed by Jodrell Bank/MERLIN personnel and investigated further by VLA personnel. These are generally called the JVAS list(s) (for Jodrell Bank-VLA Astrometric Sources). 3) VLBA calibrator information - visibility data (i.e. fringe amplitudes versus baseline lengths) and maps at S- and X-band for many sources 4) The on-going surveys for VLBA calibrators 1 and 3 are available on-line, via the NRAO web pages. You can go to www.nrao.edu and click on the relevant telescopes. Item 2 may also be available there; I haven't checked. I have an early version of the first JVAS list, which was published some time ago. I don't know the status of #4. However, most of what you need to know appears to be already available. 0839+187 is in the VLA manual (#1) and in the VLBA list of maps (#3). Here's the listing from the VLA calibrator manual which I have (which is about a year old; they probably update it from time to time - I can find out if necessary): 0842+185 J2000 A 08h42m05.094155s 18d35'40.990151" Aug98 0839+187 B1950 A 08h39m14.084300s 18d46'27.275000" ----------------------------------------------------- BAND A B C D FLUX(Jy) UVMIN(kL) UVMAX(kL) ===================================================== 20cm L P P P P 1.40 6cm C P P P P 1.00 3.7cm X P P P P 0.81 2cm U S S S S 0.60 Note that both B1950 and J2000 positions are given. I'm not sure which is the most fundamental, but in this case, I suspect they took the J2000 position from our (or USNO's) VLBI results. The date of the flux density measurements is not given here. The "A B C D" header is for the different configurations of the VLA, where A is the most spread out and D is the most compact. (If you are not familiar with this, ask Nancy - she worked there for several years while it was being built). "P" means the source is a primary calibrator at that frequency and array configuration, meaning it is unresolved. "S" means secondary calibrator, usually (I think) because they don't know enough about it. There are also data and maps at both S- and X-band in the VLBA calibrator data base for 0839+187. The source has some structure. You should see for yourself. Also of interest is that the VLBA calibrator search option lets you check for several sources in the vicinity of interest. There are several other compact sources, some with nice looking cores, within a few degrees. These might make good position reference objects for 0839+187. What is the angular range over which Jupiter has a significant bending effect? I assume that S- and X-band are frequencies at which you hope to observe. It might be a good idea to try to get more VLBA information about this object. We could try to include it in one of the RDV experiments (but the data might be sparse) or we could make a VLBA proposal to study it explicitly. I could help with this (proposal and analysis), but you and your friends would have to make the scientific explanation about why we NEED to observe it (and perhaps the nearby calibrators). (The VLBA has more proposals than they have time to observe.) Hope this is helpful, Dave